The protocol amends the Agreement on Investment Encouragement and Protection signed in 2001, "creating a new legal basis for stepping up cooperation," the report said.

The signing accompanied an investment conference in the Mekong Delta town near Kep which followed the inauguration of the final border marker between the two countries. It also coincided with the 45th anniversary of diplomatic relations.

During the conference, Hun Sen vowed to improve the investment climate in Cambodia and said his government particularly welcomed Vietnamese investors, the report said.

VNA said the Vietnamese premier called for maintaining regular dialogues between government agencies of the two countries to ease "difficulties and obstacles" for business.